Many industrial processes involve the manufacture of particles and the properties of the item of manufacture (pharmaceuticals, paint, food, chemicals, etc) depend heavily on the size of the particles used. However, there does not currently exist any method for on-line monitoring of particles smaller than 1 um.
The most common method for measuring such small particles, Dynamic Light Scattering, requires that the sample be still, and therefore must be performed off-line, not in flowing media. The reason for this is that Dynamic Light Scattering operates by trying to determine the Brownian motion of the particles to derive estimates of their size measurements. Thus, if the sample is not still, any movements, such as flow, will make it impossible to measure meaningful Brownian motions of the particles. Further, these Dynamic Light Scattering techniques measure speckle patterns produced as the laser light strikes a particle. These are very weak signals that must be integrated for a fairly long period of time to obtain a reliable signal upon which to calculate a particle size estimate. Accordingly, it typically takes several minutes to compute a particle size estimate using this technique, and it is therefore not well-suited to on line computations.
Still further, when the particles are not monodisperse (i.e., all of substantially one size), signals measured from movements of the larger particles can tend to dominate and obscure the weaker signals measured from movements of the smaller particles to the extent that the smaller particles are not properly measured, or not even detected at all.
There are current laser diffraction techniques that can measure particles in a flowing medium, but they cannot measure particle sizes less than about 500 nm. Laser diffraction measures the angular spread light scattered by the particles from a collimated laser beam. Particles smaller than a wavelength, typically less than a few hundred nanometers in diameter scatter light into a wide range of angles. Particles much smaller than the optical wavelength scatter light in the same pattern and cannot be distinguished by size.
There is a need for improved methods and systems capable of performing on line calculations of particle size distributions and particle concentrations. Further, there is a need for improved methods and systems capable of performing particle size distributions and particle concentrations of small particles flowing in a colloid. It would be desirable to include calculations of particles size distributions and particle concentrations to include particles having sizes less than 1 μm. It would further be desirable to perform these calculations and determinations on line, in line or at line. It would be further desirable to perform these calculations rapidly, on the order of a few seconds, or less.
There is also a need for improved methods for providing estimations that are smoothed to remove computational artifacts and therefore provide more accurate and definite values for particle size distribution and particle concentration values that can be more readily read and ascertained by a user.
There is a continuing need for fast and accurate methods of measuring particle size distribution of small particles, particularly for use in online applications, for real time or near-real time calculations of measurements during performance of a process where small particles are employed. Even for offline applications, it would be desirable to provide faster, more accurate methods of measuring particle size distributions.